Field
Example aspects described herein relate generally to voltage rectifier circuits, and more particularly, to methods, apparatuses and systems that employ a voltage rectifier circuit having a low-drop diode substitute with minimal loading, to capture the peak voltage of an alternating current source.
Description of the Related Art
FIG. 1 shows a circuit 101 that is used to capture the positive peak voltage of an alternating current (AC) source 102. The output current of the AC source 102, which has certain source impedance 106, is converted to direct current by a diode 103. The output voltage of the diode 103 is captured by a capacitor 105, which is slowly dissipated by a high-value resistor 104 when the output voltage of the AC source 102 is low or zero.
The circuit 101 has some limitations. First, the diode 103 has a significant voltage drop which can be problematic when the AC signal is in the low-volts range. Because of this, voltage Vout is approximately equal to the peak voltage of the AC source 102 minus the diode voltage drop. For a PN silicon diode, the voltage drop is about 0.7 volts. Assuming that the AC source 102 has a peak voltage of about 3 volts, this voltage drop can lead to a deviation from the peak voltage of about 23%. Second, this voltage drop varies with temperature. Even the voltage drop for a Schottky diode, which is generally smaller than 0.7 volts, is temperature dependent. Third, the source impedance 106 preferably must be kept quite low such that when diode 103 conducts during the peak voltage and the peak current is high, the voltage drop across the source impedance 106 also degrades voltage Vout. However, keeping the source impedance low often is difficult or expensive to do.
Resistor 104 generally has a high resistance value to slowly “bleed down” the capacitor 105 when the AC source 102 voltage is low or zero. As a result, during the peak input voltage, a current surge must supply all the charge drained away by resistor 104 during the non-peak time.